Ok, you installed the App? Did you follow the instructions from the Website?
Install the app and open it. Agree to the Terms. Select TWRP Flash. Select your device from the device list (fp2) and choose a version. The file will download to your Downloads folder. Browse to and select the file. Tap on Flash to Recovery.
Than switch off your device. Switch it on again by holding the power button + volume up buttom at the same time. You should boot now into TWRP.